\begin{tikzpicture}
    \tkzDefPoints{0/0/B, 3.4/0/C, 1.7/2/A, 1.7/0/D}

    \tkzDrawPolygon(A,B,C)
    \tkzDrawSegments(A,D)
    \tkzMarkRightAngle(A,D,B)
    \tkzLabelPoints[above](A)
    \tkzLabelPoints[below](B,C,D)
\end{tikzpicture}

